The conventional method of producing a liquid cooled cylinder block is to sand-cast it, either with temporary tooling or with a permanent mold. With these methods, the mold is made by packing or ramming molding sand around a pattern. The mold is usually made in two parts so that the pattern can then be withdrawn. When the pattern is withdrawn, the imprint of the pattern provides the cavity which ultimately is filled with metal to form the casting. If the casting is to be hollow, then additional patterns, typically called cores, must be placed in the mold cavity to form the interior surfaces of the casting. Thus, the void between the mold and the core eventually becomes the casting. A molten metal of the proper composition and temperature is poured into the mold with gravity usually being employed to cause the metal to flow into the mold. After removing the casting, any adhering sand, scale or other foreign material is removed. Machining is typically necessary to correct other defects in the casting.
When the temporary tooling method is utilized, a new pattern must be made every time a cast cylinder is made. The pattern is usually made from wood when a small quantity of castings need to be made; but for larger quantities, aluminum, magnesium or certain hard plastics are employed.
With the permanent mold sand-casting method, a more expensive, permanent pattern is used, which produces a casting having improved dimensional accuracy. However, this method still does not maintain tolerances as close or sections as thin as are possible with the die-casting method.
The above conventional manufacturing methods are extremely labor-intensive and expensive. The packing of the sand, the withdrawal of the pattern, and the pouring of the metal are all done by hand. In addition, the machining necessary to clean up the parts after production of the casting requires additional labor and expense.
Another common manufacturing method used in various applications is die-casting. The dies usually consist of two blocks of steel, each containing a part of the cavity, which are locked together while the casting is being made and drawn apart when it is ready for ejection. Retractable and removable metal cores are used to form internal surfaces. Inserts can be cast into the piece by placing them on locating pins in the die. Die-casting differs from ordinary permanent-mold casting in that the molten metal is forced into the molds by pressure and held under pressure during solidification. The die-casting cycle consists of the following steps: 1) closing and locking the dies; 2) forcing the metal into the die and maintaining the pressure; 3) permitting the metal to solidify; 4) opening the die; and 5) ejecting the casting.
There are several advantages to the die-casting process. All-metal mold, external-pressure castings have close tolerances, sharp outlines and contours, fine smooth surfaces, and a high rate of production accompanied by low labor cost. Fine sections and excellent detail can be achieved, together with long mold life.
However, in the past it has not been possible to die-cast liquid cooled cylinder blocks, because the molten metal would enter the ports of the cylinder block and fill up the inside of the cylinder. One solution to this problem is the use of metal cores, which are used extensively in die-castings. However, provision must be made for retracting the metal cores, usually before the die is opened for removal of the casting. It is very important that the direction of the core-retracting motions be either a straight line or a circular arc. The configuration of a typical cylinder block's ports is such that the cores are unable to be retracted. With the sizing and configuration of the cylinder, it was impossible to utilize core pins to prevent metal from entering the inside of the cylinder, because there was no means of removing the core pins. Consequently, liquid cooled cylinder blocks have not been manufactured with the die-casting method in the past.
The present invention addresses these and many other problems associated with the currently available manufacturing methods for liquid cooled cylinder blocks.